Advanced Reviews

The DFT/MRCI method employs a few empirically adjusted global parameters for modifying the CI Hamiltonian matrix elements. Benchmark calculations attest to its remarkably good performance for excited‐state energies and other spectral properties at moderate computational expense.

This review outlines the role of hyperconjugative interactions in the structure and reactivity of organic molecules. After defining the common hyperconjugative patterns, we discuss the main factors controlling the magnitude of hyperconjugative effects, including orbital symmetry, energy gap, electronegativity, and polarizability. The danger of underestimating the contribution of hyperconjugative interactions are illustrated by a number of spectroscopic, conformational, and structural effects. The stereoelectronic nature of hyperconjugation offers useful ways for control of molecular stability and reactivity. New manifestations of hyperconjugative effects continue to be uncovered by theory and experiments.